Pneumatic springs have been proposed already which comprise a plunger rod entering sealingly in a cylinder with pressurized gas, and having a guiding damping piston which divides the cylinder into two chambers communicating with each other by means of an axial passage through the piston.
Damped pneumatic springs of the kind set forth can be used for opening and closing vehicles or machines bonnets, actuating doors, controlling seats or desks level, etc..
According to an object of the present invention there is provided an electrical contact device suitable for detecting the end position of a telescopic system which is a pneumatic spring such as above set forth.
According to the present invention, there is provided an electrical switch comprising a cylinder with a closed bottom end, and in which a piston is slidably mounted, this bottom and piston constituting respectively the fixed and the movable contact of the switch, being electrically insulated one from the other and connected to the terminals of an electric circuit which is either closed or broken if the piston after having moved over its whole stroke engages the bottom of the cylinder or is spaced apart from it. Such a contact could be done merely through direct engagement of the bottom by the piston; nevertheless for manufacturing tolerances and slows dampering grounds, it is better to use between them an electrically conducting flexible member such a spring acting as a resilient abutment, which may be fixed at will on the piston or on the bottom.
According to an embodiment of the present invention, the cylinder is made of a conducting material and is permanently in electrical contact with the piston, whereas the bottom, also of a conducting material is fixed to said cylinder by means of a crown of insulating material, which besides may be acting as sealing gasket for the telescopic system. Alternatively, the insulation between bottom and piston could be located over the bottom, i.e. between the bottom and the cylinder, or provided by the cylinder itself, which then would be made of insulating material, at least at its end portion adjacent to the bottom.
The above discussed electrical circuit including the switch according to the present invention, comprises preferably a signal generating member, which accordingly will be actuated by the closing of the switch, in other words the piston having achieved its stroke, the circuit acting accordingly as a end position detector of the telescopic system.